1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly to a pixel structure of a thin film transistor liquid crystal display.
2. Description of Prior Art
Liquid crystal display (LCD) becomes increasingly popular due to its low radiation and compact size, and thin film transistor LCD (TFT LCD) is a mainstream display product in the market due to its contrast and viewing angle.
Since liquid crystals are non-luminous materials, the light source of the TFT LCD is a backlight light source, and the backlight light source can pass through the materials of each layer of the TFT LCD such as a polarizer and a color filter to provide a display brightness approximately equal to 10% of the brightness of the original light source. Since such brightness is insufficient, an increase of the brightness of the backlight module can increase the brightness of the pane, which will also increase the power loss of the panel module. Although increasing the aperture ratio of a display panel will improve the display effect of the panel, finding a way of increasing the aperture ratio for pixels of the display panel is still a major research subject for display panel manufacturers.
Referring to FIG. 1 for the schematic view of a prior art pixel structure, the pixel structure includes a TFT structure 1a, a scan signal line 3a formed by a first metal conductive layer, a shielding bar 2a, and a common electrode 4a, an active region 5a, a data signal line 6a formed by a second metal conductive layer, and a pixel electrode 7a formed by a transparent conductive layer. The storage capacitor is manufactured by a common electrode 4a formed by the first metal conductive layer and an overlap region 8a corresponding to a source electrode of the TFT structure 1a. The shielding bar 2a is provided for preventing a light leak and shielding extra light of the backlight module in the LCD, so that the light sources between pixels will not interfere with each other, and the display contrast can be improved. However, in a specific area, the aperture ratio according to this design is not too high, because the overlap region 8a required for forming the storage capacitor will occupy some regions of the pixels and the shielding bar 2a will lower the aperture ratio. Such design cannot comply with the market requirements for a higher resolution of the display panel (or a smaller pixel size).
Referring to FIG. 2 for the schematic view of another prior art pixel layout, the pixel structure of this prior art is basically the same as the prior art illustrated in FIG. 1 and includes a TFT structure 1a a scan signal line 3a formed by a first metal conductive layer, a common electrode 4a, an active region 5a, a data signal line 6a formed by a second metal conductive layer, and a pixel electrode 7a formed by a transparent conductive layer, and the storage capacitor is made by a common electrode 4a formed by the first metal conductive layer and an overlap region 8a corresponding to a source electrode of the TFT structure 1a. The major difference between such design and the prior art illustrated in FIG. 1 resides on that when the second metal layer is coated, a passivation layer 11a is coated by a chemical vapor deposition process, and then coated with an organic insulating layer 10a having a low dielectric constant, and finally plated with a transparent conductive layer (such as the passivation layer 11a, the substrate 12a, and the gate insulating layer 13a illustrated in the cross-sectional view of Section C-C in FIG. 3). The purpose of producing the organic insulating layer 10a is to lower the parasitic capacitance produced by the data signal line 3a and the pixel electrode 7a to avoid the occurrence of a crosstalk. Since the structure illustrated in FIG. 2 has a higher aperture ratio than the prior art structure illustrated in FIG. 1, the pixel design requires an additional area for the storage capacitor of the pixel, and such design used in a high-resolution panel still needs further improvements.